In a silver halide photographic element or material, a silver image is formed from silver halide following exposure and development. Silver halide photographic elements can comprise additional coated chemical components such as filter dyes and antifoggants that improve performance. Such components are often coated together with high-boiling organic solvents as small dispersion particles. The high-boiling solvents not only may aid in the dispersion and coating of beneficial components but also may improve properties or performance of such components.
In a silver halide color photographic element or material, a color image is formed when the element is given an imagewise exposure to light and then subjected to a color development process. In the color development process silver halide is reduced to silver as a function of exposure by a color developing agent, which is oxidized and then reacts with coupler to form dye. In most color photographic elements the coupler or couplers are coated in the element in the form of small dispersion droplets. Couplers are commonly dispersed and coated together with one or more high-boiling organic solvents, often referred to as coupler solvents. The high-boiling solvents may aid in dispersion preparation and coating and may beneficially alter the properties of couplers or of the dyes formed therefrom. For example, the proper choice of a high-boiling coupler solvent can increase coupler activity or improve dye thermal or light stability.
Many photographic elements or materials contain, in addition to imaging couplers, image-modifying couplers that release a photographically useful group from the coupling site upon reaction with oxidized color developer. Such image-modifying couplers are also commonly and adventitiously dispersed and coated together with one or more high-boiling solvents. In color photographic elements UV absorbing dyes, filter dyes, interlayer scavengers, antihalation dyes, antifoggants, stabilizers and other chemical components are also commonly dispersed and coated together with one or more high-boiling organic solvents.
It is usually desirable that a high-boiling solvent or coupler solvent remain in the layer in which it is coated and not wander into other layers or into processing solutions. Such wandering can produce unexpected or detrimental effects in a layer in which the high-boiling solvent was coated or in other layers of a multilayer photographic element. High-boiling solvents of low water solubility (e.g., less than about 6 mg/L) usually have adequate resistance to undesirable wandering. High-boiling solvents with a reasonably high degree of polarity are also desirable to aid in the dissolution and the dispersion of somewhat polar photographic chemicals, such as couplers or dyes. Solvents of high polarity can also provide improved dye hues. In addition, it is desirable that high-boiling solvents have reasonably low viscosity (less than about 500 centipoise). Low viscosity can aid in dispersion preparation and can result in smaller dispersion particles. Small dispersion particles can enhance coupler activity, reduce light scattering and can enhance dye-covering power.
There are numerous references to high-boiling solvents in the photographic art. A variety of types of high-boiling solvents are disclosed in Research Disclosure, December 1989, Item 308119, p 993, in U.S. Pat. Nos. 4,731,320, 4,900,655 and 5,451,492 and in European Patent 232,770. Ester type high-boiling solvents are disclosed in U.S. Pat. Nos. 4,080,209 and 4,873,182 and in British patent 2,217,470. None of these references discloses the structures or the advantageous use of the high-boiling solvents of the present invention. The high-boiling solvent 2-phenethylbenzoate, which while outside the scope of this invention may represent the closest prior art, is disclosed in photographic elements in U.S. Pat. Nos. 5,372,922, 5,594,047 and 5,618,657. Syntheses of high-boiling solvents of this invention are described in Chem. Lett. 4, 625 (1992), 3, 515 (1994) and 2, 141 (1995), but utilization in a photographic element is not disclosed.
There has been a need for high-boiling organic solvents that provide good dye hue but which will not diffuse from photographic layers to a significant extent during processing. These solvents must have low water solubility, low viscosity and moderate-to-high polarity. It is difficult to identify the structural features that lead to high-boiling solvents that satisfy these requirements. Furthermore, there has been a need to identify high-boiling solvents which are safe and in themselves are environmentally benign and whose decomposition products are environmentally benign.